Metal containers are generally of either two-piece or three-piece construction. Two-piece containers are typically manufactured by a drawing and ironing process to produce a container having a continuous bottom and sidewall to which a separate end piece is connected on the open end thereof to form a closed container. Three-piece containers are typically manufactured from metal roll stock that is cut into strips having a width that will substantially define the height of the resultant container and a length which will effectively define its diameter. Each strip is then formed into a cylindrical shape and the opposing edges of the strip are attached by processes known in the art, such as welding. With this type of construction, two end pieces must be separately attached to the open ends of the cylinder to form a closed container.
A key portion of the construction process for both two- and three-piece containers involves attaching at least one end piece to seal the container. In establishing the connection, typically a flange is formed on the open end(s) of the container to receive the end piece(s). The flange, which is most often a continuation of the sidewall of the container, is formed and configured to yield a desired angular relationship with respect to the sidewall. This angular relationship may vary depending upon, in part, the particular end-piece attachment method to be utilized. Regardless of the end orientation of the flange and the attachment method to be utilized, it is desirable to have a flange of substantially uniform width in order to obtain an adequate seal between the flange and the end piece attached thereto.
One method often used to secure an end piece to a flanged end of a container is by curling. An end piece, typically having a hooked outer edge, is placed on the flanged end of the container. After properly positioning the end piece relative to the flange, the flange and the end piece are curled together as is well known in the art to seal the container. In the event a nonuniform flange is used in this particular attachment process, the potential exists that there may not be a sufficient amount of flange around certain portions of the perimeter of the container to effectively perform curling operations (i.e., to properly interconnect the flange and the end piece), thereby yielding an undesirable seal in these areas.
An alternative method for attaching an end piece to the flanged end of a container is through use of a snap-on lid. In the snap-on method, the flange is typically configured such that the flange edge is downwardly oriented to a desired degree and shape and the lid has a ring-like ridge or other similar surface such that when the lid is placed over the flange, the ridge will intimately engage the lower or underside of the flange. Although not necessarily required, quite often the lid is of a slightly smaller diameter than that of the perimeter of the outer, downwardly oriented edge of the flange. Consequently, the flange-engaging portion of the lid is forced outward and/or the flange edge is forced inward when the lid is placed over and "snapped" onto the container. As can be appreciated, if a nonuniform or improperly oriented flange is used with this attachment method, the potential also exists for an inconsistent or insufficient container flange/lid interface, thereby yielding an ineffective seal in the corresponding areas.